It is already known practice to provide a degassing passage leading from the manifold chamber to the degassing chamber, whereby bubbles of air or gas which are conveyed by the cooling liquid and which tend to collect in the top of the manifold chamber may be evacuated via said passage to the expansion chamber.
However, if the liquid inlet tube to the heat exchanger opens out into the top of the same manifold chamber, turbulence is created in this region which tends to prevent the bubbles from coalescing there, which renders the degassing passage almost useless.
Preferred embodiments of the present invention provide a simple, cheap and effective solution to this problem.